...this phone is 'natural" Siemens phone
Regarding to Benq, is the other story.
I writed manny, manny times, in my posts, how to unlock S-Gold phones. If your firmware version is lower with FW.36, use the direct calculation methode using papuautils software and service cable (not data cable) like serial data cable for C55 phones, DCA500 or USB to serial cable DCA510 with the minor modification (insert two resistors between pin 5, 7 and pin 2 in the Lumberg connector - phone connector).
If your firmware is highter, use supplimentary the Viper (or BSreader midlet) to unlock your phone. See in attachemment how to use it.
BTW: If you unlocked with success, please announce me, because I need from you to make fullflash backup to help the other member from this forum to rewiev his C75i phone...
If not, contact me in PM to help you to unlock you phone.
Download software:
SiMoCo: http://rapidshare.com/files/19546575/SiMoCo.rar
Servicecable (include papuautils): http://rapidshare.com/files/44149250/Service_cable.rar
dagos